This invention relates to azeotropic compositions and particularly to quaternary mixtures of trichlorotrifluoroethane, methylene chloride, methanol and cyclopentane.
The electronic industry with its highly diversified needs has sought solvents which can effectively remove rosin fluxes from printed circuit boards and remove emulsion residues from computer aluminum discs prior to coating. In both instances, removal of these impurities is essential to achieve maximum reliability of the printed circuit's assembly and computer systems. The solvent used for cleaning surfaces must not only be highly effective for removing the undesired residues but must, for commercial applications, be stable, nonflammable and be compatible with electronic components and material of construction (aluminum, e.g.). In addition, where possible the solvent mixtures should desirably form an azeotrope; a constant boiling mixture which should remain stable under vapor degreasing conditions.
Several of the chlorofluoroethanes have attained widespread use as specialty solvents in recent years, in particular trichlorotrifluoroethane has become widely used. This compound is a relatively low boiling liquid (CCl.sub.2 FCClF.sub.2, 47.6.degree. C.), which is nontoxic and nonflammable, and which has satisfactory solvent power for greases, oils and the like. It has therefore found frequent use for cleaning electronic hardware and other substrates including electric motors, compressors, photographic film, lithographic plates, instruments, gauges, sound tape, and a variety of other substrates, often of the kind where aqueous cleaning mixtures are preferably avoided.
In cleaning printed circuit boards, various prior art solvent cleaning mixtures are presently recognized as effective agents; but in the area of removal of buffing compounds from memory discs, they suffer from at least the following disadvantage: they are not miscible with the chemicals to be removed; have poor wetting abilities; limited penetration; and inadequate washability to remove particulate contaminants from crevices. Other disadvantages in prior art mixtures occur, for example, where highly chlorinated solvents such as 1,1,1-trichloroethane are used. Although effective in wetting residue, these solvents hydrolyze in the presence of moisture and white metal substrates, forming hydrochloric acid, a highly corrosive chemical.
A number of binary as well as ternary azeotropic (constant boiling) mixtures have been employed for the purpose of cleaning electronic hardware which afford many of the advantages obtainable with solvent mixture. Illustrative of such azeotropic systems are the azeotrope of 1,1,2-trichlorotrifluoroethane and methylene chloride, (disclosed in U.S. Pat. No. 2,999,817); the ternary system trichlorotrifluoroethane, methyl alcohol and methylene chloride (disclosed in U.S. Pat. No. 3,400,077) and the ternary system of 1,1,2-trichloro-1,2,2-trifluoroethane, methylene chloride and cyclopentane (disclosed in U.S. Pat. No. 3,607,767). However, the solvencies of these binary or ternary compositions are less than desired and the solvents leave deposits on aluminum discs.
A need therefore exists for a cleaning composition of improved solvency and compatibility particularly in cleaning memory discs-aluminum substrates prior to coating.
In particular, a need exists for a cleaning composition which mixes readily, and dissolves and floats residues of buffing material (typically an emulsion comprised of oil, surfactant, water-glycol and particulates). Thus, the solvent mix must contain a hydrocarbon solvent to dilute the glycol based buffing material and to float particulates; an aliphatic alcohol to wet hydrophylic surfaces; a strong solvent to cut oily, greasy residues; a solvent having vapors six times heavier than air to minimize the diffusion rate of the other solvent vapors; impact stability and safety (non-flammability). Such mixture exhibits greater solvency power and greater wettability of hydrophobic and hydrophylic surfaces. This is important where emulsion type buffing compound residues need to be removed from aluminum discs, lenses and glass molds.